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Design, synthesis, and physical properties of the intergrowth compound Eu$_2$CuZn$_2$As$_3$

Xiyu Chen, Ziwen Wang, Wuzhang Yang, Jia-Yi Lu, Zhiyu Zhou, Shanshan Wang, Zhi Ren, Guang-Han Cao, Shuai Dong, Zhi-Cheng Wang

TL;DR

This work demonstrates a design strategy for discovering magnetic topological materials by intergrowth, synthesizing Eu$_2$CuZn$_2$As$_3$ as a hybrid of EuCuAs and EuZn$_2$As$_2$. The compound shows a sequence of antiferromagnetic transitions with an easy-plane ground state, significant negative magnetoresistance, and a nonlinear anomalous Hall response linked to spin textures and a potentially topological band structure. First-principles calculations identify a FA-type AFM ground state with SOC-induced band gaps and band inversion, suggesting magneto-topological phases emerge from the intergrowth architecture. Overall, the results highlight interblock coupling as a lever to tune magnetic, transport, and topological properties, establishing a roadmap for discovering new magnetic topological materials through structural hybridization.

Abstract

The rational combination of existing magnetic topological compounds presents a promising route for designing new topological materials. We report the synthesis and comprehensive characterization of the layered quaternary intergrowth compound Eu$_2$CuZn$_2$As$_3$, which combines structural units of two known magnetic topological materials, EuCuAs and EuZn$_2$As$_2$. Eu$_2$CuZn$_2$As$_3$ exhibits an antiferromagnetic ground state with successive magnetic transitions: quasi-two-dimensional ordering at $T_\mathrm{M} = 29.3$\,K, long-range antiferromagnetic ordering at $T_\mathrm{N} = 19$\,K, and spin-reorientation at $T_\mathrm{SR} = 16.3$\,K. The stepwise magnetic transitions manifest as plateau-like anomalies in the heat capacity. These transitions originate from multiple superexchange pathways and periodic variation of interplane Eu-Eu distances in the intergrowth structure. Charge transport shows a pronounced resistivity increase above $T_\mathrm{N}$ followed by minimal change below the ordering temperature. Magnetic fields rapidly suppress this resistivity rise, yielding significant negative magnetoresistance. Remarkably, Eu$_2$CuZn$_2$As$_3$ inherits the nonlinear anomalous Hall effect characteristic of its parent compounds. Energy evaluations of collinear spin configurations reveal a lowest-energy state with ferromagnetic coupling between Eu planes in EuCuAs units while maintaining antiferromagnetic coupling within EuZn$_2$As$_2$ units. The corresponding electronic structure displays potentially topologically nontrivial features. Our work demonstrates the efficacy of structural hybridization for discovering novel magnetic topological materials and establishes a general strategy for materials discovery.

Design, synthesis, and physical properties of the intergrowth compound Eu$_2$CuZn$_2$As$_3$

TL;DR

This work demonstrates a design strategy for discovering magnetic topological materials by intergrowth, synthesizing EuCuZnAs as a hybrid of EuCuAs and EuZnAs. The compound shows a sequence of antiferromagnetic transitions with an easy-plane ground state, significant negative magnetoresistance, and a nonlinear anomalous Hall response linked to spin textures and a potentially topological band structure. First-principles calculations identify a FA-type AFM ground state with SOC-induced band gaps and band inversion, suggesting magneto-topological phases emerge from the intergrowth architecture. Overall, the results highlight interblock coupling as a lever to tune magnetic, transport, and topological properties, establishing a roadmap for discovering new magnetic topological materials through structural hybridization.

Abstract

The rational combination of existing magnetic topological compounds presents a promising route for designing new topological materials. We report the synthesis and comprehensive characterization of the layered quaternary intergrowth compound EuCuZnAs, which combines structural units of two known magnetic topological materials, EuCuAs and EuZnAs. EuCuZnAs exhibits an antiferromagnetic ground state with successive magnetic transitions: quasi-two-dimensional ordering at \,K, long-range antiferromagnetic ordering at \,K, and spin-reorientation at \,K. The stepwise magnetic transitions manifest as plateau-like anomalies in the heat capacity. These transitions originate from multiple superexchange pathways and periodic variation of interplane Eu-Eu distances in the intergrowth structure. Charge transport shows a pronounced resistivity increase above followed by minimal change below the ordering temperature. Magnetic fields rapidly suppress this resistivity rise, yielding significant negative magnetoresistance. Remarkably, EuCuZnAs inherits the nonlinear anomalous Hall effect characteristic of its parent compounds. Energy evaluations of collinear spin configurations reveal a lowest-energy state with ferromagnetic coupling between Eu planes in EuCuAs units while maintaining antiferromagnetic coupling within EuZnAs units. The corresponding electronic structure displays potentially topologically nontrivial features. Our work demonstrates the efficacy of structural hybridization for discovering novel magnetic topological materials and establishes a general strategy for materials discovery.

Paper Structure

This paper contains 11 sections, 2 equations, 7 figures, 2 tables.

Table of Contents

  1. INTRODUCTION
  2. METHODS
  3. RESULTS AND DISSCUSSION
  4. Structrual analysis
  5. Magnetism
  6. Heat capacity
  7. Charge transport
  8. Magnetic energies
  9. Electronic structure
  10. CONCLUSIONS
  11. Additional $\rho_{xx}(H)$ curves

Figures (7)

  • Figure 1: (a) Crystal structure of Eu$_2$CuZn$_2$As$_3$ visualized using VESTA software 54VESTA. (b) SEM (top) and optical microscope (bottom) images of Eu$_2$CuZn$_2$As$_3$ single crystals. (c) XRD pattern ($\theta-2\theta$ scan) of the Eu$_2$CuZn$_2$As$_3$ single crystal showing exclusively (00$l$) reflections. The peaks adjacent to the main diffraction peaks are the $K\alpha2$ reflections, while unlabeled weak peaks correspond to unfiltered $K\beta$ reflections.
  • Figure 2: (a) Temperature-dependent in-plane magnetic susceptibility $\chi_{ab}(T)$ of Eu$_2$CuZn$_2$As$_3$ under different magnetic fields ($H\parallel ab$). The inset shows the splitting between ZFC (dash line) and FC (solid line) curves below 19 K under a 2 mT field. (b) Out-of-plane magnetic susceptibility $\chi_c(T)$ under various applied fields ($H\parallel c$). The inset shows the temperature derivative $d\chi_c/dT$, highlighting the magnetic transitions in Eu$_2$CuZn$_2$As$_3$. (c) $\chi_c(T)$ measured at 0.1 T (black, left axis) with corresponding CW analysis for the 100--300 K temperature range (right axis). (d) In-phase component ($\chi^{\prime}_{ab}$) of the ac magnetic susceptibility ($H\parallel ab$) at various frequencies. The inset presents $d\chi^{\prime}_{ab}/dT$ at 1356 Hz. (e) Field-dependent magnetization $M(H)$ at 5 K for both in-plane (black diamonds) and out-of-plane (red dots) field orientations. The inset displays the magnetization $M(H)$ in the low-field range ($\mu_0H \leq 60$ mT). (f) In-plane magnetization curves $M_{ab}(H)$ measured under small applied fields at various temperatures. The inset shows the field derivative $dM_{ab}/dH$.
  • Figure 3: (a) Temperature dependence of the zero-field heat capacity $C_\mathrm{p}(T)$ of Eu$_2$CuZn$_2$As$_3$. The red curve represents a fit combining the Debye and Einstein models in the temperature range 50--190 K. The inset plots $C_\mathrm{p}/T$ versus $T$ below 40 K. (b) Temperature dependence of the magnetic specific heat $C_\mathrm{mag}(T)$ (orange) and the derived magnetic entropy $S_\mathrm{mag}(T)$ (blue). (c) $C_\mathrm{p}(T)$ at various applied magnetic fields. The inset plots $C_\mathrm{p}/T$ versus $T$ at 0 T (black), 0.5 T (red), and 1 T (blue). (d) Temperature derivative of the heat capacity, $dC_\mathrm{p}/dT$, in the range 10--40 K.
  • Figure 4: (a) Zero-field anisotropic resistivity $\rho_{xx}(T)$ of Eu$_2$CuZn$_2$As$_3$ with current applied along the $c$-axis ($\rho_c$, red) and $ab$-plane ($\rho_{ab}$, black). The inset shows the temperature derivative $d\rho_{xx}/dT$. (b) Field-dependent Hall resistivity $\rho_{xy}(H)$ at various temperatures. (c,d) Temperature dependence of the in-plane resistivity $\rho_{ab}(T)$ under different (c) in-plane and (d) out-of-plane magnetic fields. (e,f) Temperature dependence of the out-of-plane resistivity $\rho_c(T)$ with the magnetic field applied (e) parallel to the $ab$-plane and (f) parallel to the $c$-axis. (g,h) Magnetic field dependence of (g) $\rho_{ab}$ with $H\parallel ab$ and (h) $\rho_c$ with $H\parallel c$ measured at 10 K, 23.5 K, 30 K, and 50 K.
  • Figure 5: (a) Key interplane Eu-Eu couplings mediated by CuAs planes ($J_1$) and Zn$_2$As$_2$ layers ($J_2$). Positive coupling coefficients denote AFM (A) interactions, while negative values indicate FM (F) coupling. (b-e) Proposed magnetic configurations for Eu$_2$CuZn$_2$As$_3$: (b) AA-type ($J_1>0$, $J_2>0$), (c) FA-type ($J_1<0$, $J_2>0$), (d) AF-type ($J_1>0$, $J_2<0$), (e) FF-type ($J_1<0$, $J_2<0$).
  • ...and 2 more figures